I will say the best time probably is do your research in the summer before senior year then start going to company intro sessions and start applying for jobs in early fall semester. This way, hopefully you won't have to think much about it in Spring semester. That's how I had tackled it and worked well for me.
Hannah recommends the following next steps:
In my opinion I would start applying that last semester. I would definitely recommend taking a internship and building a good relationship with a potential employer. Performing well within that internship will help with the job search.